1. Field of the Invention
This invention relates in general to data storage systems, and more particularly to a method and apparatus for performing position error signal conditioning of LTO media servo format written-in velocity variation.
2. Description of Related Art
Data loss is a serious threat to companies of all sizes, and catastrophic data loss can destroy a business. But most data loss isn""t the result of a big disaster, it""s caused by human error, viruses, and disk malfunctions. A suitable backup routine provides the best protection against data loss of all kinds. And tape technology remains the most efficient and cost-effective means to perform system backup, whether for a small business or a global 24xc3x977 operation.
Tape remains unrivaled in terms of cost and capacity for data storage, and should play an increasing crucial role in corporate data protection strategies. No other technology offers the same combined low cost and high capacity advantage of tape. While other technologies may offer strengths in one or more areas, overall, they do not meet the entire set of customer needs that tape addresses.
Tape drives make backup fast, easy, reliable and affordable. Speed is critical because your data is constantly growing while the time available for backup is shrinking. Even the slowest tape drive writes 1 MB per second and the fastest 30 MB per second, which means a 200 GB backup can be completed in less than two hours. Furthermore, unlike other storage methods, tape drives offer a range of media that allows you to back up all the data on a small to medium-sized server. Tape backup also captures system setup information, as well as data, allowing an entire system to be restored in the event a disaster strikes. Also, backups can be scheduled to occur automatically at a time determined to be most convenient.
Another area where tape storage excels is when it comes to data protection. Tape has proved itself a reliable medium, and tape drives themselves have never been more reliable. Easily portable, tapes have the added advantage of being simple to remove and store offsite, so keeping a disaster recovery copy is less of a burden.
In terms of affordability, tape is the most cost-effective way to store large amounts of data per gigabyte of storage. The compact size of tape cartridges also helps keep down your storage costs.
Nevertheless, the tape industry has become fragmented with the proliferation of formats and technologies that have overly complicated customer buying decisions. Therefore, LTO Technology (or Linear Tape-Open Technology) has been developed to combine the advantages of linear multi-channel bi-directional tape formats in common usage today with enhancements in the areas of timing-based servo, hardware data compression, optimized track layouts and high efficiency error correction code to maximize capacity and performance.
The new LTO tape product uses a tape format that has longitudinally prewritten servo tracks. The servo tracks provide a timing-based track-following position error system. The tracks contain a repeated pattern of recorded flux transitions that occur as grouped bursts of 5, 5, 4, and 4 transitions. The timing between the sets of 5-bursts and between sets of 4-bursts provides the position information for the track following system. Additionally, the individual transitions within the 5-bursts are phase-shifted in a manner that encodes longitudinal position information (LPOS) into the servo tracks. By detecting the phase-encoded LPOS information, the tape transport system determines the tape position relative to landmarks lengthwise down the tape. The LPOS information is used to keep track of the longitudinal position of data records written onto or read from the tape, and is used to locate those data records when the reading or writing process temporarily stops. The LPOS location of data files on tape is also stored in the volume control data for use to locate the data files during a later tape cartridge load for reading, or for write-appending new files onto the end of the last file written to the tape. The LPOS data is thus used as the primary positional information for the tape transport servo control system, it is used in the decision process for starting and stopping the tape, and for backhitching the tape in order to position the read-write heads at the beginning of a data record at the required velocity and track position which allows the start of a new data transfer operation.
In determining the Position Error Signal, the repeated pattern of recorded flux transitions occur as grouped bursts of 5, 5, 4, and 4 transitions. However, because of longitudinal velocity deviations during the formatting process, when the servo patterns are recorded onto the tapes, an oscillation in the PES signal will result. This oscillation will in turn degrade the performance of the track following servo system. In many cases, the problem is so severe that, it causes an intolerable number of xe2x80x98stop writesxe2x80x99 (a vibration that cause more than 5 um of tracking error signal). A direct filtering out of this oscillation on the PES is not feasible since it will cause too much loss of phase margin and make the overall tracking following servo system unstable.
It can be seen that there is a need for a method and apparatus for performing position error signal conditioning of LTO media servo format written-in velocity variation.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for performing position error signal conditioning of LTO media servo format written-in velocity variation.
The present invention solves the above-described problems by filtering only the signals demonstrating velocity deviations.
A method in accordance with the principles of the present invention includes detecting flux transitions in servo signal bursts to produce detected servo signals, filtering detected servo signals exhibiting velocity vibrations and computing position error signals using filtered detected servo signals and detected servo signals not requiring filtering.
Other embodiments of a method in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the flux transitions comprise a series of A-shaped burst pairs.
Another aspect of a method of the present invention is that the series of A-shaped burst pairs extend along the media.
Another aspect of a method of the present invention is that the signals exhibiting velocity vibrations are flux transitions in the burst of servo signals that have a spacing that depends on the precision of the formatter velocity.
Another aspect of a method of the present invention is that the signals not exhibiting velocity vibrations are flux transitions in the burst of servo signals that have a spacing that is dependent upon the fixed structure of the servo burst formatter head.
Another aspect of a method of the present invention is that the flux transitions in servo signal bursts include a first and second burst forming a first A-shaped burst pair, a third and fourth burst forming a second A-shaped burst pair, and a fifth and sixth burst forming a third A-shaped burst pair, wherein each burst comprises a plurality of legs and wherein each burst in a burst pair are angled toward each other, each of the A-shaped burst pairs having a spacing that is dependent upon the fixed structure of the servo burst formatter head, and the spacing between burst pairs being depends on the precision of the formatter velocity.
Another aspect of a method of the present invention is that a time measurement of the spacing between flux transitions in the third and fourth burst and between the flux transitions in the fifth and sixth burst comprises an A time interval and the spacing between the flux transitions in the second and fourth burst and between the flux transitions in the fourth and sixth burst comprise a B time interval.
Another aspect of a method of the present invention is that the B time interval exhibit velocity vibrations because of the precision of the formatter velocity, wherein the position error signal is computed according to:
PES=refxe2x88x92A/(B filtered), 
wherein A represents unfiltered A time interval servo components and B filtered represents filtered B time interval servo components.
Another aspect of a method of the present invention is that each A-shaped burst comprises at least four flux transition legs, wherein each A-shaped burst comprises at least four legs.
Another aspect of a method of the present invention is that the series of A-shaped burst pairs comprise a leading and a trailing edge, the A-shaped burst pairs providing an A-time interval measured by a servo head from the leading edge to the trailing edge of an A-shaped burst pair.
Another aspect of a method of the present invention is that each of the A-shaped burst pairs comprise a plurality of legs, wherein the legs of the burst pair are configured with a predetermined spacing at a first end and getting larger toward an opposite end at a predetermined angle to provide lateral position of the servo head.
Another aspect of a method of the present invention is that the series of A-shaped burst pairs comprise a leading and a trailing edge, the A-shaped burst pairs providing a B-time interval measured by a servo head from a leading edge of one A-shaped burst pair to the leading edge of the next A-shaped burst pair.
Another aspect of a method of the present invention is that the B-time interval is constant independent with the lateral position of the servo head.
Another aspect of a method of the present invention is that the B-time interval is modulated if the servo formatter has velocity variations during writing the format pattern, wherein the position error signal is computed according to:
PES=refxe2x88x92A/(B filtered), 
wherein A represents the A-time interval and B filtered represents the filtered B-time interval.
In another embodiment of the present invention, a tape drive is provided. The tape drive includes a magnetic recording tape having servo signal bursts of flux transitions recorded thereon, the servo bursts comprising a configuration of stripes of A spacings and B spacings, a servo head disposed proximate the magnetic recording tape for sensing the flux transitions of the servo signal bursts and a servo controller, coupled to the servo head, for receiving the sensed signals from the servo head, the servo controller further comprising a filter for filtering the B time interval servo signal components and computing a position error signal according to:
PES=refxe2x88x92A/(B filtered), 
wherein A represents unfiltered A time interval servo components and B filtered is filtered B time interval servo components.
Another aspect of a tape drive of the present invention is that the filter comprises a low pass filter.
Another aspect of a tape drive of the present invention is that the filter comprises a notch filter.
Another aspect of a tape drive of the present invention is that the filter comprises filtering software implemented in the servo controller.
In another embodiment of the present invention, an article of manufacture comprising a program storage medium readable by a computer is disclosed. The medium tangibly embodies one or more programs of instructions executable by the computer to perform a method for performing position error signal conditioning of LTO media servo format written-in velocity variation, wherein the method includes detecting flux transitions in servo signal bursts to produce detected servo signals, filtering detected servo signals exhibiting velocity vibrations and computing position error signals using filtered detected servo signals and detected servo signals not requiring filtering.
Another aspect of an article of manufacture of the present invention is that the flux transitions comprise a series of A-shaped burst pairs.
Another aspect of an article of manufacture of the present invention is that the series of A-shaped burst pairs extend along the media.
Another aspect of an article of manufacture of the present invention is that the signals exhibiting velocity vibrations are flux transitions in the burst of servo signals that have a spacing that depends on the precision of the formatter velocity.
Another aspect of an article of manufacture of the present invention is that the signals not exhibiting velocity vibrations are flux transitions in the burst of servo signals that have a spacing that is dependent upon the fixed structure of the servo burst formatter head.
Another aspect of an article of manufacture of the present invention is that the flux transitions in servo signal bursts include a first and second burst forming a first A-shaped burst pair, a third and fourth burst forming a second A-shaped burst pair, and a fifth and sixth burst forming a third A-shaped burst pair, wherein each burst comprises a plurality of legs and wherein each burst in a burst pair are angled toward each other, each of the A-shaped burst pairs having a spacing that is dependent upon the fixed structure of the servo burst formatter head, and the spacing between burst pairs being depends on the precision of the formatter velocity.
Another aspect of an article of manufacture of the present invention is that the spacing between flux transitions in the third and fourth burst and between the flux transitions in the fifth and sixth burst comprises an A time interval and the spacing between the flux transitions in the second and fourth burst and between the flux transitions in the fourth and sixth burst comprise a B time interval.
Another aspect of an article of manufacture of the present invention is that the B time intervals exhibit velocity vibrations because of the precision of the formatter velocity, wherein the position error signal is computed according to:
PES=refxe2x88x92A/(B filtered), 
wherein A represents unfiltered A time interval servo components and B filtered represents filtered B time interval servo components.
Another aspect of an article of manufacture of the present invention is that each A-shaped burst comprises at least four legs.
Another aspect of an article of manufacture of the present invention is that the series of A-shaped burst pairs comprise a leading and a trailing edge, the A-shaped burst pairs providing an A-time interval measured by a servo head from the leading edge to the trailing edge of an A-shaped burst pair.
Another aspect of an article of manufacture of the present invention is that each of the A-shaped burst pairs comprise a plurality of legs, wherein the legs of the burst pair are configured with a predetermined spacing at a first end and a larger predetermined spacing at an opposite end to provide lateral position of the servo head.
Another aspect of an article of manufacture of the present invention is that the series of A-shaped burst pairs comprise a leading and a trailing edge, the A-shaped burst pairs providing a B-time interval measured by a servo head from a leading edge of one A-shaped burst pair to the leading edge of the next A-shaped burst pair.
Another aspect of an article of manufacture of the present invention is that the B-time interval is constantly independent with the lateral position of the servo head.
Another aspect of an article of manufacture of the present invention is that the B-time interval is modulated if the servo formatter has velocity variations during writing the format pattern, wherein the position error signal is computed according to:
PES=refxe2x88x92A/(B filtered), 
wherein A represents the A-time interval and B filtered represents the filtered B-time interval.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.